Sounds like what is commonly referred to as Level Funded, Self-Insurance. As a rule, any funds returned to the employer become a taxable event and if there were employee contributions, the employer would need to calculate their portion of the refund and return. As such, most employers will apply the surplus as a future payment, thus avoiding the tax event and refunding to employees.
I am a little confused by what you refer to as “no group health insurance contract” in your statement. There should be documents available, such as SBC’s, a SPD, stop loss contract, etc. Can you expand?